全文获取类型
收费全文 | 39043篇 |
免费 | 3997篇 |
国内免费 | 3188篇 |
专业分类
化学 | 8317篇 |
晶体学 | 439篇 |
力学 | 1701篇 |
综合类 | 373篇 |
数学 | 4759篇 |
物理学 | 10388篇 |
综合类 | 20251篇 |
出版年
2024年 | 108篇 |
2023年 | 327篇 |
2022年 | 772篇 |
2021年 | 913篇 |
2020年 | 798篇 |
2019年 | 757篇 |
2018年 | 792篇 |
2017年 | 1087篇 |
2016年 | 1199篇 |
2015年 | 1242篇 |
2014年 | 1933篇 |
2013年 | 2337篇 |
2012年 | 2284篇 |
2011年 | 2342篇 |
2010年 | 1869篇 |
2009年 | 2156篇 |
2008年 | 2149篇 |
2007年 | 2607篇 |
2006年 | 2263篇 |
2005年 | 2112篇 |
2004年 | 1786篇 |
2003年 | 1657篇 |
2002年 | 1525篇 |
2001年 | 1282篇 |
2000年 | 1241篇 |
1999年 | 1143篇 |
1998年 | 977篇 |
1997年 | 870篇 |
1996年 | 807篇 |
1995年 | 673篇 |
1994年 | 658篇 |
1993年 | 569篇 |
1992年 | 523篇 |
1991年 | 427篇 |
1990年 | 364篇 |
1989年 | 350篇 |
1988年 | 349篇 |
1987年 | 226篇 |
1986年 | 148篇 |
1985年 | 113篇 |
1984年 | 70篇 |
1983年 | 43篇 |
1982年 | 75篇 |
1981年 | 46篇 |
1980年 | 37篇 |
1979年 | 50篇 |
1978年 | 46篇 |
1977年 | 29篇 |
1976年 | 27篇 |
1973年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Yang Woo Shin 《Operations Research Letters》2004,32(4):364-373
We consider a single server queue with disasters where the arrivals of customers and disasters are correlated. When a disaster occurs, it removes all the customers in the system and there requires repair time for the system to be operated normally. The stationary queue length distribution at the embedded points and at an arbitrary time are presented. 相似文献
93.
The form of the probability density derived from the evolution in time of a previously truncated frequency distribution of animal Liveweights is of interest in animal husbandry. Truncated frequency distributions arise when the heavier animals are sold for slaughter and the lighter animals retained. The demands of modern quality assurance schemes require that, given information on animal growth, the farmer is able to estimate the number of animals that would meet the specifications at some time in the future after truncation. Assuming that animal growth can be described by a linear stochastic differential equation, we derive an explicit expression for the probability density of animal Liveweights at any time after the truncation of an initial Gaussian density. It is shown that this probability density converges rapidly to a Gaussian density, so that after about 20 days of typical growth rates for lambs, the resulting density is practically indistinguishable from Gaussian. 相似文献
94.
The distributions of limit cycles of cubic vector fields (P2, Q3) are considered in this paper, where P2 and Q3 are polynomials of x and y of order two and three, respectively. It is possibly seven different distributions of limit cycles given in [1]. We now prove that in which three kinds of distributions are impossible and other four kinds all can be realized by concrete vector fields of (P2,Q3). Some related results are also given. 相似文献
95.
用热传导方程控制激光辐照温度,建立了一种新回归方程以控制激光辐照硬化深度,选用卡尔丹公式列热传导方程及同归方程联立求解,可得到同时满足一定的硬化深度及表面最高温度双重要求的工艺参数,此种方法可作为激光硬化处理工艺参数的控制或预报,对本合金铸铁的激光硬化处理,其表面温度的下限应大于其熔点温度,即以表面产生微熔的快速冷凝处理为宜,并以选取低功率慢扫描为最佳。 相似文献
96.
K. S. Birdi 《Colloid and polymer science》1997,275(6):561-566
The surface tension versus temperature data of homologous series of n-alkanes and n-alkenes is analyzed. Critical temperatures are shown to be predicted from these data, with a very high precision, after some
corrections are made. The corrections are shown to arise from the effect of the critical pressure on the extrapolated data
to surface tension approaching zero.
Received: 29 October 1996 Accepted: 13 December 1996 相似文献
97.
Space time-index plots for probing dynamical nonstationarity 总被引:3,自引:0,他引:3
We propose a simple method to efficiently probe dynamical nonstationarity in observed time series. In a space time-index plot, the density distributions as a function of normalized time-index are V-shaped due to nonstationarity. We show that this method is workable for short data sets and typical examples are illustrated. 相似文献
98.
安徽省豹猫的分布和数量 总被引:3,自引:0,他引:3
应用皮张收购资料的统计和访问调查、野外实地考察等方法,研究了豹猫在安徽省的分布、数量及历史变化。 相似文献
99.
Asymptotic chi-squared test statistics for testing the equality of moment vectors are developed. The test statistics proposed are generalized Wald test statistics that specialize for different settings by inserting an appropriate asymptotic variance matrix of sample moments. Scaled test statistics are also considered for dealing with nonstandard conditions. The specialization will be carried out for testing the equality of multinomial populations, and the equality of variance and correlation matrices for both normal and nonnormal data. When testing the equality of correlation matrices, a scaled version of the normal theory chi-squared statistic is proven to be an asymptotically exact chi-squared statistic in the case of elliptical data. 相似文献
100.